


this is the first time you've been this old

by Morcai



Category: Katekyou Hitman Reborn!
Genre: Coming of Age, Gen, Growing Up, Organized Crime, box animal contemplation, deciding what the title 'Vongola Decimo' means, have you ever realized natsu looks nothing like an actual lion
Language: English
Status: Completed
Published: 2019-11-01
Updated: 2019-11-01
Packaged: 2021-01-16 18:16:31
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,430
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21275585
Author URL: https://archiveofourown.org/users/Morcai/pseuds/Morcai
Summary: Tsuna and Natsu, growing up.





	this is the first time you've been this old

**Author's Note:**

> obviously, my round 1 fill for the remix exchange! the prompt was "Natsu grows from a cub to a lion". In some ways, this is a sibling fic to my previous contemplation of Tsuna-as-Decimo, [_taste of dried up hopes in your mouth_](https://archiveofourown.org/works/7750909) but it functions as a standalone.

When they were all young, and box animals were just another strange part of the future they had been thrown into, the silly, unthreatening look of Natsu’s form never drew comment. It suited Tsuna, after all, and it was better than the disasters from the first times he opened the Vongola Sky Box.

These days, though, Natsu is almost monstrous, both hyperrealistic and cartoon-flat at once, too much to look at for very long. He’s a housecat with a mane of flame and knife-edged outlines, more vivid than any other box animal, too sharp against the world.

Now, as Tsuna grows, fifteen-sixteen-seventeen, skidding ever closer to fluency in the dual mafia languages of Italian and violence, it’s becoming clear how out of place Natsu is.

There’s something a little cartoony about most of the box animals, but it’s the cartoon comedy of a kangaroo in boxing gear, the flashiness of Lussuria’s peacock, Bester’s more-than-natural stillness. Natsu is different. The closest any box animal comes is Uri, and she’s still more _ real _ than Natsu is. Uri is a leopard cub who plays at being a kitten sometimes. Natsu is all not-quite, not quite a housecat, not quite a lion cub, not quite anything real.

Tsuna sympathizes.

* * *

Timoteo has a health scare halfway through Tsuna’s final year of high school, and that’s that. The day after the news arrives, Tsuna is no longer a student, his bags are packed, and he’s on a plane to Italy. The Vongola can’t afford an image of weakness, and with Timoteo hospitalized and recovering slowly, Tsuna’s presence will deter other Families from testing them.

Tsuna’s caught between pride that Reborn didn’t have to explain any of that to him, and shame that his first reaction to hearing of Timoteo’s hospitalization was _ oh fuck, the Vinceni negotiations_.

When he lands in Palermo, it’s a similar mix of emotions, dread of what’s coming, shame that he still hasn’t just told the Vongola to go to hell and leave him alone, relief to be off the plane, delight at being back in Italy.

Tsuna has loved Italy since the first time Timoteo called him to Palermo over a school break. He blames Reborn, and the way that his tutor has irretrievably destroyed his ability to parse the difference between something to love and something to fear. 

The next several months are hectic, as Tsuna, who has been running the Vongola’s delicate expansion into Asia, suddenly becomes solely responsible for the entirety of the Family.

Maybe that’s part of why, in spite of the fact that Natsu spends more time out of the ring than in it, he doesn’t notice Natsu changing. The fact no one else notices, well. Tsuna chalks that up to the fact that no one has really wanted to look at Natsu for years.

He’s not sure when it actually happens. He just knows that one day he glances up from another report, trying to soothe the pounding in his forehead, and looks at Natsu, sprawled on Timoteo’s desk, and sees rounded ears where there were once triangles, a heavier build, The flame of Natsu’s mane and the tip of his tail is dimmer, closer to the body.

All the sudden, Natsu looks like a lion cub, not a lion by grace of not quite being anything else.

Tsuna breathes out, drops the report. Reaches one hand to his Box Animal, feels Natsu bump a sturdy jaw into his trembling fingers.

Natsu is still too vivid, but some of the cartoon has worn away.

Tsuna doesn’t know what it means, this change in Natsu’s shape, and he’s not sure it’s a good thing.

* * *

Natsu keeps shifting, in fits and starts, as Tsuna wraps his hands into the heartlines of the Vongola, shows his face, becomes more than the myth of the Vongola’s Japanese heir. Timoteo returns to his position, but everyone knows, now, that he won’t rule much longer.

There are more and more eyes on Tsuna, more and more eyes on the lion-creature that walks by his side.

Xanxus is the first one to say anything. Tsuna wouldn’t have guessed that, would have thought it would be Reborn, or Hayato, or even Byakuran who first mentioned it. But then again, Reborn doesn’t bother to comment on things he doesn’t care about, or thinks are improving Tsuna. Byakuran is as busy as Tsuna is, these days, and so they don’t see much of each other.

As for Hayato...that’s probably a mixture of the careful way Tsuna’s family has learned to not-really look at Natsu, and the fact that Hayato is, like the overachieving whackjob he’s always been, balancing his duties as right hand to the crown prince of the Vongola with completing a dual degree in chemical engineering and physics.

So it’s Xanxus who is the first to say anything. It happens on a day like any other, except that Tsuna has escaped to the Varia compound to clear profit projection analyses and employee retainer fees from his skull.

That’s something he didn’t expect at fourteen, when Reborn told him he’d be a mafia boss. It’s a lot less murder and extortion, a lot more like running a very successful and fairly self-sufficient business.

“You’re an idiot, baby capo,” Xanxus says, when Tsuna mentions as much. “Business is all it’s ever been.”

Tsuna rubs his thumb against the heavy steel of the Vongola Gear, and thinks he disagrees. He doesn’t say anything though, and eventually Xanxus just snorts, slouches deeper into his throne. It looks disrespectful, but Tsuna’s never been stupid about Xanxus’ heart, and he can see the gleam of _ attention _ in those red eyes.

“You need something?” the head of Tsuna’s assassins says, and Tsuna’s mouth tightens. _ Just business _ covers a lot of things for the Vongola, and there’s a very clinical cost-benefit analysis of a job for the Varia on Tsuna’s desk in Timoteo’s office, waiting for Tsuna to get back to it and decide if he’s passing it along.

“A spar,” Tsuna says.

The gleam of attention sharpens, which is all the warning Tsuna gets before Bester’s roar hits him like a sledgehammer.

With that, it’s _ on_, and Tsuna leaps backwards out of Xanxus’ office, not willing to get caught in his cousin’s own space, where there are no doubt traps laid for anyone stupid enough to challenge him there.

Fighting Xanxus is, like it’s been since the very first time, a test of every single bit of Tsuna’s Will, ability, intelligence, and Flame. It’s fast-paced and terrifying and it _ hurts _ every time that Tsuna doesn’t evade a shot quite well enough, but it’s clean, too.

Sparring with Xanxus is just sparring with Xanxus. Nothing more, and certainly nothing less. Tsuna calls to Natsu without thinking about how he’s changed, and the two of them fall into and out of Cambio Forma, attacking and defending, all Flame and fabric and fierce resonance.

It ends in a draw, like it always does. Xanxus isn’t quite willing to go far enough that he might kill Tsuna these days, and Tsuna isn’t willing to freeze the whole battlefield to win a concession from Xanxus. As soon as they stop moving, Natsu flops down on the ground, panting.

He’s changed again, the childish rosettes and stripes he’d carried just months ago starting to fade. He’s bigger too, turning to all mismatched proportion, paws too-big for his body.

“You’re growing up, baby capo,” Xanxus says, eyeing Natsu. It’s clear what he means, that he understands what he sees. Tsuna grimaces.

“I don’t think I want to be.”

* * *

Tsuna leans his head against the wall, listens to the party inside. He's twenty-three today.

If he can make it through two more years, he'll live to be the same age as the version of him who broke everyone who loved him on the altar of saving the world.

He's not sure how he feels, that it's looking increasingly likely that he'll live that long. That he’ll live _ past _ that long.

"What the hell am I doing?" Tsuna asks the night sky. When he doesn't get an answer, he just sighs, raises his hand, looks at his ring. It’s the same as always—fire, Natsu, gem, Vongola name—except for how it’s totally different from when he first put it on, almost a decade ago.

Natsu's been changing on the ring, too. There's not much of the cute creature in a sun visor left in the square-jawed lion that now stares back from above the Vongola name and crest. When Tsuna calls him, Natsu is all gangly adolescence, childish coloring fading to dust-gold fur.

They're both growing up, turning into such dangerous creatures.

* * *

“It’s the Cardassi, Boss,” Hayato says, and Tsuna breathes out, traces the grain on the top of his desk with his eyes, forces down the fury he feels at having his suspicions confirmed.

The Cardassi. Recent allies, one of the last negotiations primarily conducted by Timoteo before he retired. Making their money off of fashion, primarily. A small Family.

A small Family that has taken the Vongola’s goodwill, and used it to kill fifteen of their people, and to leave Takeshi bleeding.

Tsuna would like to be a good person about this, would like to cling to what he told Giotto, would like to turn his back on the legacy of the Vongola in how to handle this. Would like to do something other than mark this first year of his reign by deciding to tear a whole family out of existence by its roots.

He’d like to do that, except for how he really wants to bare his teeth and have them all die screaming.

“Where are they?” Tsuna asks, and he feels like he’s already in Hyper Dying Will Mode. There’s a pure, clean line to make the Cardassi answer for what they’ve done, Tsuna can see it, and he’s going to _ take _ it.

“Naples,” Hayato says, and Tsuna knows that his right hand is looking at him with worry. That’s fine. Hayato should probably be worried. Tsuna isn’t going to like himself much when this is over. Which isn’t going to stop him from doing it.

“Get me transport,” Tsuna says, standing from his desk. Natsu stirs from where he’s been lying, and Tsuna eyes his Box Animal, takes in Natsu’s rangy, savage lines, the way his armoring has changed over the years. Natsu is starting to look more and more like Bester, more and more like the original design for the Sky Lion boxes. It’s as unnerving as it is comforting.

* * *

All of the most important growing Tsuna has ever done has happened in the middle of a battle. This is no exception.

Tsuna hadn’t expected the ambush, which is his own fucking fault for not paying attention to the intel Haru has been passing him. But he thought no one would be stupid enough to lay hands on his people so soon. He’d _ thought _ that the goddamned _ spectacle _ he made of himself over the Cardassi would be enough to keep his people safe for a few more months.

Instead, here he is, fighting his way out of a crumpled wreck, the smell of Antonio’s blood heavy in his mouth. He can hear Lucia screaming in his head, shouting to _ stay under cover_, because he’s _ irreplaceable_.

Tsuna doesn’t care. Antonio, who told the same three terrible jokes every time he drove Tsuna anywhere, was irreplaceable too.

Keeping low, Tsuna finally manages to shove the door to his car open, and before he leaves the safety of B7 armor and shattered bulletproof glass, he presses his lips to his ring. 

Natsu responds, quick as thought, and the familiar warmth of the Moda Defensa settles around Tsuna, peculiarly light and heavy all at once.

With that, Tsuna rolls out of his car, assessing the ambush as soon as he can lay eyes on whoever it is who’s trying to kill him this time.

He doesn’t recognize them. That’s not a surprise—there are so many crime families, and while Tsuna keeps up with his closest allies, his deepest enemies, and his income bracket, there just isn’t enough time to know every Family in Italy.

More importantly, though, he can see Chiara trying to extract herself from her motorcycle, Adrien checking a pistol as he hunkers down behind another car in the convoy—and he can see that no matter how hard they try, the two of them, and everyone else here who has sworn to keep him safe, are going to die.

_ Unacceptable_, Tsuna’s Will snaps, and his Flame is roaring, _ not my people_, and he can _ feel _ Natsu respond. He’s never done it before, but when Tsuna tears off his mantle and _ throws_ , aiming between Chiara and the three pistols being leveled at her, he _ knows _it will work, that Natsu will protect her.

The bullets reflect off of fluttering black fabric, and Tsuna turns his attention to counterattacking, lets the Cambio Forma lapse. 

There’s a roar as soon as he feels it fade, deep and furious and it rings through Tsuna’s Flame like a tuning fork, like a bell.

The attackers go stiff, still, paralyzed. 

Tsuna breathes, stands, calculates police response times and how much he cares about keeping secrets. The best thing to do is burn these men down, leave nothing but a messy crash that the police aren’t paid enough to investigate. It wouldn’t be so different from how he cleaned up the Cardassi infiltrators, anyway.

The problem, Tsuna realizes, as he listens to his heart thunder in his ears, the echo of Natsu’s roar in his Flame, is that he doesn’t want to. He knows he _ should_, but he doesn’t _ want _ to, not like with the Cardassi.

He’s had ten years to learn to love the Vongola, and to learn how their reputation was built, how it’s maintained. Now he has to figure out how to live with that.

He doesn’t want to have to live with that. He’s never wanted it. Not since the first time Reborn told him about the Vongola.

Tsuna feels Natsu come to a halt beside him, a sense of pressure, of heat at his hip. He doesn’t need to look to know that Natsu has changed again, filled out more, that the rough edges have finally smoothed away.

He can feel it, just like his Flame, burning still and certain. This is what they are now, like it or not. Head of the Vongola Famiglia and responsible for its people, a king, a lion fully grown.

They get to decide what that means.


End file.
